This invention relates to photoconductive compositions and members containing photoconductive substances and spectral sensitizers. More particularly, this invention relates to photoconductive compositions and materials containing photoconductive substances and azacyanine spectral sensitizers.
Hitherto, many organic compounds have been known as photoconductive substances for electrophotographic sensitive materials. Among them, some compounds have been confirmed to have relatively high sensitivity. Under existing circumstances, however, there are very few cases wherein an organic photoconductive substance has been practically used for the electrophotographic sensitive materials. Organic photoconductive substances have many excellent properties as compared with inorganic photoconductive substances, and have possibilities of various utilizations in the field of electrophotography. For example, production of transparent photosensitive films, flexible sensitive films and light-weight sensitive films capable of easy handling becomes possible by use of organic photoconductive substances. Further, they have characteristics which cannot be expected in inorganic photoconductive substances, for example, a film-forming property for production of sensitive materials, surface smoothness, and selectivity of charge polarity when applied to an electrophotographic copying process, etc. However, organic photoconductive substances have not sufficiently contributed to the field of electrophotography up to now in spite of having such various excellent characteristics in many viewpoints, because they generally have low sensitivity to light.
Generally, in case that the sensitivity of the photoconductive substance itself is low and is in a range of short wavelength spectra, certain substances may be added in order to increase the sensitivity and to transfer the sensitivity to a range of longer wavelength spectra.
As sensitizers for improving the sensitivity, though many organic substances have been known, they each have disadvantages together with advantages and there is no completely satisfactory sensitizer in the viewpoint of improving the sensitizing effect. Therefore, it is a subject desired for a long time by persons skilled in the art to develop more effective spectral sensitizers for organic photoconductive substances.
For example, thiacarbocyanines containing an electron attractive group, such as halogen, nitro, etc., as described in Japanese Pat. Publication No. 2 632 144 have already been known as a spectral sensitizer for the organic light-conductive substance. Although this spectral sensitizer has the advantage that it improves sensitivity characteristics because it contains an electron attractive nitro group, etc., it suffers the disadvantages that it is inferior in solubility, and, when a coating film is formed using the sensitizer, causes deposition of crystals, etc., making it difficult to obtain a uniform coating film, and that the uneven coating film markedly reduces the light sensitivity.